Theoretical equilibration time is supported by measurement study of residence time at dilution sampling on fine particulate matter emissions from household biofuel burning

Household biofuel burning contributes a large proportion of fine particulate matter (PM_2.5), black carbon (BC), and organic carbon (OC) emissions in many parts of the world. Dilution sampling has been widely used to characterize PM_2.5 emitted from biofuel burning. The residence time in the dilution chamber is a key parameter for accurate sampling. However, residence time has not yet been adequately characterized for biomass combustion. In this work, we investigated the effects of residence time of dilution sampling on PM_2.5 emissions from a typical Chinese household stove burning typical biofuels including three major crop wastes and one type of wood. The filter based measurements indicated that the emission factors for PM_2.5 and its main chemical components such as OC, EC, Cl⁻, and K⁺ did not vary with the residence time over the range of 1–80 s. Theoretical estimation of average time scale for achieving dynamic equilibrium (τ_s) between the gas and particle phase in the dilution sampling system was less than 1 s. Both the measurement study and theoretical simulations indicated that dilution sampling with a residence time of 1s can provide adequately reliable results for PM_2.5 emissions from biofuel burning under the condition of these experiments. A simple way to estimate the equilibration time based on measured average PM_2.5 concentration was proposed. Recommendations are provided for the residence time for dilution sampling of accurate measurements of PM_2.5 emissions from biofuel burning.